1. Field of the Invention
The present invention relates to a device comprising an optical circuit constituted using an optical waveguide, that is, an optical waveguide device, and a manufacturing method therefor.
2. Description of Related Art
A device, which constitutes an optical circuit using an optical waveguide, has been known for sometime. In this application, this kind of device is referred to as an optical waveguide device.
As a conventional optical waveguide, the device disclosed in xe2x80x9cCurrent Status and Future Trends in Planar Lightwave Circuit Technologiesxe2x80x9d Masao KAWACHI, NTT RandD Vol. 43, No. 11, 1994, pp.1273-1280, for example, is well known.
In the optical waveguide disclosed in this paper, an under cladding, core, and upper cladding are each formed using a silicon oxide layer. In an optical waveguide, the refractive index of the cladding (under cladding and upper cladding) must be made higher than the refractive index of the core. In the above-mentioned technology, the refractive index of the cladding and the refractive index of the core are made different by making the compositions of the silicon oxide layers different. In the above-mentioned technology, the difference in specific refractive index between the cladding and the core is around 0.25-2%. Further, in this optical waveguide, the thickness of the silicon oxide layers of the under cladding and the upper cladding, respectively, is around 15-30 xcexcm. Meanwhile, the cross-sectional dimensions of the core are a width of around 4-10 xcexcm, and a height of around 4-10 xcexcm.
In a process for manufacturing an optical waveguide, first, a layer constituting an under cladding, and a layer constituting a core are sequentially deposited by spraying silicon oxide glass particulates of a grain diameter of 0.1 xcexcm on top of a silicon wafer. The raw material gas of these glass particulates have silicon tetrachloride as the main constituent, and comprises GeO2 as a dopant. Glass particulates are produced by hydrolyzing this raw material gas in an oxyhydrogen flame. The composition of the glass particulates in the under cladding layer and core layer can be made different by changing the concentration of the GeO2 dopant.
Next, a transparent silicon oxide glass layer is formed by heating these glass particulate layers in an electric furnace at a high temperature of 1,250xc2x0 C. or higher. Since the composition of the glass particulates in the under cladding layer and core layer will differ, the refractive indices of these layers will also differ.
Thereafter, the core is processed using reactive ion etching.
Finally, an upper cladding is formed by depositing a layer that covers the upper surface and side surfaces of the core layer using glass particulates of the same composition as the under cladding, and once again applying the same heat treatment as described hereinabove.
In a conventional optical waveguide such as the one described hereinabove, the difference in specific refractive index between the cladding and the core is only 2% or less. That is, in this optical waveguide, the drawback was that the difference in specific refractive index was small.
When this difference in specific refractive index is small, since the radius of curvature of the curved portion of the core must be increased (around 1-25 mm), the optical circuit constituted using this optical waveguide must become larger overall.
Further, when this difference in specific refractive index is small, since the cross-sectional dimensions required for satisfying single mode conditions become large, for example, around 4-10 xcexcm, fabrication becomes difficult using ordinary semiconductor manufacturing equipment for semiconductor integrated circuits.
Furthermore, in a manufacturing process of a conventional optical waveguide such as that described hereinabove, since a layer constituting an under cladding, and a layer constituting a core, and a layer constituting an upper cladding each had to be deposited, the number of processes was large, and manufacturing costs were high.
An object of the present invention is to provide an optical waveguide device with a large difference in the specific refractive index of the core and the claddings.
Another object of the present invention is to provide a manufacturing method for inexpensively manufacturing via a simple process an optical waveguide device with a large difference in specific refractive index of the core and the claddings.
An optical waveguide device related to the present invention comprises an under cladding, which is formed using silicon oxide; a core, which is formed on top of the under cladding with silicon, and which propagates light; and an upper cladding, which is formed using silicon oxide, and which covers the side surfaces and upper surface of the core.
According to an optical waveguide device related to the present invention, because a core is formed using silicon, and an under cladding and an upper cladding are formed using a silicon oxide layer, the difference in specific refractive index between the core, and the lower and upper claddings can be increased. Therefore, the radius of curvature of the curved portion of a core can be lessened, and the cross-sectional dimensions can be reduced.
A manufacturing method for an optical waveguide device related to the present invention comprises a process for forming a core by etching a silicon layer of a Silicon-on-Insulator substrate using a mask pattern, and, in addition, for exposing a silicon oxide layer as an under cladding; and a process for forming an upper cladding by depositing a silicon oxide layer on the surfaces of the core and under cladding.
According to the manufacturing method for an optical waveguide device related to the present invention, because an optical waveguide device is manufactured by using a Silicon-on-Insulator substrate, it is possible to reduce the number of manufacturing processes.